Hydrocarbon jet fuel containing decaborane and alkanols or phenols



3,086,355 Patented Apr. 23, 1963 3,086,355 HYDROCARBGN JET FUELCONTAEWING DECA- BORANE AND ALKANGLS R PHENOLS Blanchard L. Michel,Munster, Ind, and Fred K. Kawahara, Park Forest, 111., assignors toStandard Oil Company, Chicago, 111., a corporation of Indiana NoDrawing. Filed Feb. 19, 1959, Ser. No. 794,236

Claims. (Cl. 60-354) This invention relates to hydrocarbon fuels for jetand rocket engines, and more particularly relates to a hydrocarbon fuelfor such engines containing one or more particular additives for thepurpose of decreasing the tendency of the fuel to form and deposit gumat high temperatures.

Modern jet engines impose special restrictions on the type of fuelswhich may be satisfactorily employed in their operation. This isbecause, in turbo-jet engines, the turbine and compressor may operate atshaft speeds of about 8,000 rpm, resulting in the generation ofconsiderable heat at turbine and compressor shaft bearings. Bearinglubricants thus must not only reduce friction but must carry away largeamounts of frictional heat. In the supersonic air-speed region wheremost military designed jets are operated, conventional air-cooled oilheat exchangers are useless, and consequently the growing trend is touse the engine fuel supply as a coolant for the lubricat ing oil.

This use of fuels as a lubricating oil coolant gives rise to a seriousproblem. In oil-fuel heat exchangers the fuel is subjected to quite hightemperatures, on the order of 400-500 F. or higher, for a relativelyshort period of time. At these conditions, if the fuel is thermallyunstable and particularly if it is susceptible to oxidative gumformation, the heat exchanger may become fouled with gum and henceineffective, and as a result oil temperatures may rise and bearingfailures may occur. over, suspended gum and soluble gum which form inthe exchanger are carried downstream with the fuel, where they plug fuelfilters and combustor nozzles. Ultimately, engine roughness, cycling,reduced performance, and combustor warping may result from suchplugging. Even complete engine flame-out may occur.

A similar problem arises in liquid-fueled rockets. Liquid fueled rocketsmay circulate the incoming hydrocarbon fuel around the combustionchamber before the fuel is injected into the chamber. Should gum or cokedeposition occur during this short-time high-temperature exposure, thecombustion chamber would overheat and ultimately cause destruction ofthe rocket engines and perhaps the rocket vehicle itself.

A primary object of the present invention is to provide a hydrocarbonfuel for jet or rocket engines which is inhibited against gum formationand gum and coke deposition at high temperatures. Another object is toprovide an additive or additive combination for jet and rocket fuels toenable the use of hydrocarbons which, in the absence of the invention,would be too unstable from the standpoint of gum formation to be used inthese engines. Other and more particular objects will become apparent asthe description of this invention proceeds.

in accordance with the invention, a hydrocarbon jet or rocket fuel whichnormally would tend to cause gum formation and gum or coke deposition athigh temperatures is inhibited against gum formation and deposition bythe addition thereto of a minor amount of a boron compound selected fromthe group boron hydrides. It has been further discovered in accordancewith the invention that the effectiveness of the foregoing boroncompounds is greatly enhanced when the jet or rocket fuel also containsa minor amount of an alkanol having from More- 1 to about 8, preferably1-4, carbon atoms per molecule, such as isopropanol, or a phenol of 6-8carbon atoms.

Among the boron compounds useful in accordance with the invention arethe boron hydrides, which have the formula B H and B H Boron hydridescorresponding to the first mentioned formula are polymers of thehypothetical compound EH formerly called borine, while the lattercompounds are derivatives of the hypothetical compound B H The boronhydrides are also termed boranes, and since a borane having a givennumber of boron atoms per molecule may have either of two formulae, itis conventional to include in parenthesis, after the name of thecompound, the number of hydrogen atoms per molecule. Thus according tothis nomenclature the following suggested compounds may be employed inaccordance with the invention: diborane (6), tetraborane (10),pentaborane (9), pentaborane (11), hexaborane (10), hexaborane (12),decaborane (14), etc. In general, while boranes having from 1 to about20 or more boron atoms per molecule are useful, it is preferred to use aborane having from 4 to about 12. boron atoms per molecule, since theseare relatively nonvolatile and have only a slight tendency to bepyrophoric.

The second but optional component used as an additive herein is a loweralkanol, i.e. an aliphatic alcohol having from 1 to 8 carbon atoms permolecule, preferably from 1 to 4 carbon atoms per molecule, or a phenolof 6-8 carbon atoms. Suitable alkanols include methanol, isopropanol,n-butanol, amyl alcohol, and hexanol. Suitable phenols includeunsubstituted phenol, cresol, 'etc.

The amounts of each additive which are added to a particular jet orrocket fuel depend both on the service temperature and upon the inherentstability of the uninhibited hydrocarbon fuel. Where the fuel is highlyunstable, particularly When derived from thermally cracked petroleumhydrocarbons, both additives may be used in relatively highconcentrations, while an essentially virgin fuel or hydrogenated fuelrequires very little of either. Ordinarily, the amount of boron compoundmay range from as little as 0.001 volume percent to about 5 volumepercent based on total fuel, but usually is in the range of about 0.001to 0.5%, preferably between 0.01 to 0.05% for the average JP-4 or J P-Sfuel. The amount of alcohol may be as little as 0.001 to as much asabout 20 volume percent, preferably 0.01 to 15%; the amount of alcoholmay be limited by allowable water absorption tolerances of the fuel.Since boron compounds vary considerably in molecular weight, therequired amounts thereof may be defined on the basis of moles of boroncompound per liter of hydrocarbon, and, in these terms, there may beused 0.0001 to 0.01, preferably 0.001 to 0.005 moles of boron compoundper liter (m./l.) of fuel.

The hydrocarbon fuel or base component of the inventive jet or rocketfuel consists chiefly of a liquid hydrocarbon fluid boiling in the rangeof about 150 to 650 F. usually in the range of about 150600 F. Jet androcket fuels are usually prepared to conform with various militaryspecifications, and existing jet fuels for military and civilian jetsmay be defined with reference to specification MIL-F-56l6 (JR-1), andMIL-J-5624D (JP-3, 4, and -5). JP-4, the most commonly used present day(1959) jet fuel has a 20% distillation point of 290 F. and a point of470 R, an API gravity between 45 and 57, an existent gum of 7.0 max., apotential gum of 14.0 max., and may contain a maximum of 25 volumepercent aromatics and 5 volume percent olefins. Various otherrequirements for JP-4 are described in the foregoing MIL- J5624D. Otherjet fuels are described in, for example, MIL-F-25656, MIL-F-25524A,MIL-F-S 161E, etc. Ram jet engines currently employ grade RI-l fuel (MILF-2558-B) having a 430 F. minimum initial boiling point and a 600 F.maximum end point in addition to other requirements. Hydrocarbon RP-1grade fuels for rockets are described in MILF25576A and MILF 19605(SHIPS). It is contemplated that other requirements and other types offuel may, from time to time, be substituted in whole or in part for thecurrent jet and rocket fuel definitions.

Special-purpose hydrocarbon fuels for jets and rockets, such astechnically pure alkyldicyclohexyl or alkyldecalin derivatives may alsobe inhibited against gum formation and deposition with the instantadditive or additives.

In order to establish the efficacy of the presently described boroncompounds, alone and in the conjoint presence of an alcohol, an unstablejet fuel was prepared from an ordinary JP4 hydrocarbon jet fuel to whichwas added one part by volume of a highly unstable thermal naphtha perfour parts of the JP4. This fuel base, both with and without variousinhibitors, was tested in a laboratory device for determining gumformation and deposition characteristics under short-timehigh-temperature conditions equivalent to those experienced in theoil-fuel heat exchangers of turbo-jet engines or on combustion chamberwalls of rocket engines. The test device was a thermostaticallycontrolled metal block through which ran a channel containing aremovable aluminum specimen which specimen was Weighed before and aftereach test to determine the amount of gum or coke deposition thereon.Test conditions were a block temperature of 400 F and fuel flow rate of400 ml. per hour, resulting in a fuel residence time of 12 seconds. Thetest was run for 2.5 hours. The following results were obtained:

JET FUEL HIGH TEMPERATURE STABILITY TEST RESULTS It is particularlynoted that only 0.003 M decaborane reduced deposit weight by about 70%,while volume percent isopropanol alone actually increased the depositweight. However, the combination of decaborane with isopropanol elfecteda 95% reduction in deposit weight. Moreover, the combination resulted ina fuel after testing which was water-clear and exhibited no cloudinessdue to gum or other solid formation. It is also noted that isopropanolentirely eliminated solids formed by the apparent decomposition ofdecaborane.

The foregoing test data demonstrate that by adding a boron compound,optionally together with an alcohol, to a liquid hydrocarbon jet orrocket fuel, oxidative gum formation and deposition are at leastpartially inhibited. Consequently, the fuel side of a jet engine oilfuelheat exchanger is maintained in more effective condition, with moreeffective heat exchange, than would be possible in the absence of saidadditives. Also, using the instant additives there are several benefitsto be gained in rocket or jet engines; the combustion chambers aremaintained clean and cool, and the higher heat of combustion of boroncompounds is advantageous in increasing the specific impulse of rocketfuels and in increasing the range or load-bearing capacity of jetaircraft. The boron compound and/ or the alcohol or phenol may beincorporated in the hydrocarbon fuel during manufacture or introducedimmediately before fueling the vehicle or alternatively, it may beintroduced by injecting these additives in the form of a concentrateinto the fuel just before the fuel passes into the engine. Suchconcentrate may contain at least 5 volume percent boron compound and atleast 20 volume percent alcohol or phenol, the balance (if any) beinginert for the present purpose.

We claim:

1. A jet and rocket fuel composition consisting essentially of a majorproportion of a normally liquid hydrocarbon of the jet and rocket fuelboiling range normally tending to cause gum and coke deposits at hightemperatures, from about 0.001 to about 5 volume percent of decaborane,and from 0.001 to about 20 volume percent of a member of the groupconsisting of alkanols having from 1 to 8 carbon atoms per molecule andphenols having from 6 to 8 carbon atoms per molecule.

2. The composition of claim 1 wherein said alkanol is isopropanol.

3. A jet and rocket fuel composition comprising a major proportion of anormally liquid hydrocarbon of the jet and rocket fuel boiling range (a)from about 0.001 to about 5 volume percent of decasborane and (b) fromabout 0.001 to about 20 volume percent of isopropanol.

4. The method of operating jet and rocket engines comprising burning insaid engines a fuel composition consisting essentially of a majorproportion of a normally liquid hydrocarbon of the jet and rocket fuelboiling range, from about 0.001 to about 0.5 volume percent ofdecaborane, and from 0.001 to about 20 volume percent of a member of thegroup consisting of alkanols having from 1 to 8 carbon atoms permolecule and phenols having from 6 to 8 carbon atoms per molecule.

5. The method of claim 4 wherein the alkanol is isopropanol.

References Cited in the file of this patent UNITED STATES PATENTS2,662,817 Russell et al Dec. 15, 1953 2,813,830 Trautman Nov. 19, 19572,858,339 Clark et a1 Oct. 28, 1958 2,860,167 Brown Nov. 11, 19582,866,811 Irish et al Dec. 30, 1958 2,894,830 Nerad et a1 July 14, 1959OTHER REFERENCES 43rd Report National Advisory Committee forAeronautics, pp. 2 to 4 (1957).

Schechter et al.: Boron Hydrides and Related Compounds, Callery ChemicalCo., 2nd Edition, 1954, pages 15,18, 22 and 26.

Beachall et al.: J. Am. Chem. Soc., vol. 80, pages 2943-5 (1958). 7

1. A JET AND ROCKET FUEL COMPOSITION CONSISTING ESSENTIALLY OF A MAJORPROPORTION OF A NORMALLY LIQUID HYDROCARBON OF THE JET AND ROCKET FUELBOILING RANGE NORMALLY TENDING TO CAUSE GUM AND COKE DEPOSITS AT HIGHTEMPERATURES, FROM ABOUT 0.001 TO ABOUT 5 VOLUME PERCENT OF DECABORANE,AND FROM 0.001 TO ABOUT 20 VOLUME PERCENT OF A MEMBER OF THE GROUPCONSISTING OF ALKANOLS HAVING FROM 1 TO 8 CARBON ATOMS PER MOLECULE ANDPHENOLS HAVING FROM 6 TO 8 CARBON ATOMS PER MOLECULE.
 4. THE METHOD OFOPERATING JET AND ROCKET ENGINES COMPRISING BURNING IN SAID ENGINES AFUEL COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF ANORMALLY LIQUID HYDROCARBON OF THE JET AND ROCKET FUEL BOILING RANGE,FROM ABOUT 0,001 TO ABOUT 0.5 VOLUME PERCENT OF DECABORANE, AND FROM0.001 TO ABOUT 20 VOLUME PERCENT OF A MEMBER OF THE GROUP CONSISTING OFALKANOLS HAVING FROM 1 TO 8 CARBON ATOMS PER MOLECULE AND PHENOLS HAVINGFROM 6 TO 8 CARBON ATOMS PER MOLECULE.